That is certainly != to what I wrote....

Exactly the point. In your code, each iteration of the loop assigns the next row to $_ (your while statement), then assigns the following line to $line_holder. The line assigned to $_ is never handled, so it just get's "skipped."

In any case, couldn't the whole process be reduced to

my %seen = () ;
my @uniq_rows = grep { !$seen{$_}++ } <FILE> ;
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?

Those who know that they are profound strive for clarity. Those who
would like to seem profound to the crowd strive for obscurity.
            --Friedrich Nietzsche

Er just a thought but any time ive written that code ive ended up changing it to

my @unique=map{chomp; $_{$_}++ ? () : $_} <FILE>;
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or something like it (i dont always use %_ but sometimes i do, blame ABIGAIL-II ;-)

To be honest i think that in my perl career ive only used a grep a few times. map seems to be so much more useful in that it can do grep()s job, and more as well!

Yves / DeMerphq
---
Software Engineering is Programming when you can't. -- E. W. Dijkstra (RIP)

And when i write something like that i usually change it to something like:

my %seen;
my @unique = grep {not $seen{$_}++} <FILE>;
chomp @unique;
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Or something similar. It might not be the best way to do it, but it has one advantage...

It has nothing to do with using %_. It's mostly because i'm very wary of changing $_ in map, especially since i recently got very burned by attempting such a thing...

jynx

update: at prompting, i'll mention that one could write that as:

my (%seen, @unique);
chomp( @unique = grep {not $seen{$_}++} <FILE> );
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however, i think that would iterate twice as well. Then again there's that point about premature optimization... ;-)

Update 2: after doing a benchmark, i've found that the map solution is the fastest, followed by the one-line chomp and last is the two-liner. The one-liner is sufficiently fast enough that i would still prefer it, although for readability and maintainability i might still go with the two line version. To each their own...

Thanks demerphq for the learning experience... :-)